1. Field of the Invention
The present invention belongs to the technical field of gas phase absorption. More specifically, the invention refers to a process for the removal or recovery of gaseous, volatile organic or inorganic low molecular, low polar compounds, called "VLC" in this technical field, from gaseous environments such as gas streams, typically air streams.
In the modern society, the environment suffers from various VLC sources. Industrial gaseous emissions greatly contribute to the pollution of the atmospheric environment. Human activities linked to that pollution are the following: energy production, wood and paper industries, paints and polymers, agro-alimentary industries such as gist and sugar manufacture, the petrochemical industry, etc. The olfactive nuisances generated by wastes (industry of animal by-products, animal excrements, household garbage) will add to this pollution. Furthermore, sewage purification plants are sources of bad smells.
There is a still growing interest to treat the nuisances generated by the industrial world, and especially the elimination of bad odors has considerably increased during the last years in following the general requirements of a better quality of life.
There are already technical solutions available and corresponding necessary regulations set out regarding the partial or complete removal of odors. Thus, in France, Section 17 of the decree No. 77 of Sep. 12, 1972, states that "the regulations consider in particular, on one hand, the effectiveness of available techniques and their economy and, on the other hand, the quality of the vocation and the use of environmental mediums". The regulation emerging from the laws and the decrees thus comprises the necessary tools for an adaptation to the evolution of antipollution techniques and their application.
2. Description of the Prior Art
Different deodorizing techniques are already known: odor masking, thermal oxidation with and without catalysts, active carbon adsorption, biological purification, gas-solid absorption combined with chemical washing, etc. Therefore, the treatment of odors is generally effected by washing and oxidation, by adsorption (on charcoal, natural adsorbents, synthetic adsorbents), or by biopurification.
Japanese Patent Publication No. JP-3,249,941 (application No. JP-90-0'046'450) discloses a deodorant composition for garbage and toilets comprising the reaction product of a divalent heavy metal salt such as CuCl.sub.2 and ascorbic or erythorbic acid in aqueous, isopropanol containing ammonia at 70.degree. C. for 4 hours. The reaction product is formed or deposited in powdered p-tert-butylcalix[8]arene as a support. Tests, published in this document, have shown that the deodorizing effect of said reaction product is the same with and without calixarene which acts thus as a solid support or carrier only and not as a deodorizing agent.
The document WO-A-89.08092 discloses the removal of polar hydrocarbons such as trihalomethanes from fluids, in particular from drinking water.
The ability of calixarenes for absorbing non-polar, relatively low molecular substances has already become known. Thus, the following documents disclose this finding: U.K. Patent No. 2,292,156 (separation of alkanes from a hydrocarbon mixture, using an aqueous solution of a calixarene); and WO 95 11,208 (liquid phase separation of alkenes and aromatics from a hydrocarbon stream).
Finally, the international patent publication No. WO 95/11449 discloses the use of calixarenes which are substituted by at least one redox active substituent for the detection of toxic agents such as chemical warfare agents. Another publication (JP-A-02,124,850) describes the polymerization and the use of vinyl substituted calixarenes.
Taking into account the sometimes very high volatility of the odorous VLC and the very low olfactive perception level of most of these compounds, no method and technique whatsoever affords a satisfactory solution of the problem. The industrial, continuous absorption of gaseous, bad smelling sulfur or nitrogen containing compounds from a gas stream in using pure calixarenes which are not substituted by reactive groups is neither disclosed nor suggested in the prior art.